Project Summary/Abstract HIV infects about 40 million people worldwide, among whom approximately 10% harbor chronic hepatitis B virus (HBV) co-infection. The progression of chronic HBV to cirrhosis, end-stage liver disease, or hepatocellular carcinoma is accelerated in HIV coinfection compared to chronic HBV monoinfection. Nucleos(t)ide analogues (NAs) including entecavir and tenofovir are currently approved for the treatment of chronic HBV infection. In HIV coinfection, despite HBV suppression with NAs, there is still evidence for more severe liver injury and fibrosis compared with NA-suppressed HBV monoinfection. However, the mechanisms by which HIV increases HBV replication and HBV-induced liver fibrosis are not well characterized. One of the major obstacles in HIV-HBV coinfection study has been the lack of a robust animal or co-culture model. We have extensive experience in the study of HIV-induced liver fibrosis in HCV-HIV coinfection and have parlayed this experience into relevant models for HIV-HBV co-infection. Using HIV/HBV mono-culture and novel transwell and spheroid co-culture models (up to 3 lines) developed in our laboratory, we have found that HIV increases HBV replication, HBV cccDNA levels, and enhances HBV-induced fibrosis-related gene expression in HBV HepAD38, HBV- infected NTCP-HepG2 and LX2 HSC cells. We have found that HBV and HIV infection each induce cytokine disturbances that could contribute to fibrosis. Separately, we have found that HIV enhances pyruvate production, which in turn promotes hepatic fibrosis. We hypothesize that HIV cooperatively promotes HBV-related liver fibrosis through (1) alterations in profibrogenic cytokine secretion and (2) changes in pyruvate status. To evaluate these hypotheses, we will use in vitro mono-culture, and transwell and spheroid co-culture models and verify these findings in liver and blood from in vivo humanized mice HIV/HBV coinfection models. These Aims are feasible, mechanistically grounded, and highly likely to yield results that will lead to clarification of HIV-HBV-host interactions. They are also likely to yield an array of new targets for the development of treatments designed to enhance HBV functional cure and preventing HIV-accelerated HBV liver disease progression.